1. Field of the Invention
The present invention relates generally to disks such as an optical recording disk, an optical reproducing disk or the like and, more particularly to a disk having a magnet chucking hub fixed thereto by means of a ultrasonic welding.
2. Description of the Prior Art
A known optical recording or reproducing disk is generally incorporated in a disk cartridge in which a part of the surface of the disk and a chucking hub fixed to the center of the disk are exposed through an opening formed through the disk cartridge. Upon non-use, a shutter closes the opening of the disk cartridge to hide the optical disk.
Upon use of this disk, when the disk cartridge is loaded on a recording and reproducing apparatus, the shutter is opened and a disk table is inserted into the central portion of the opening of the disk cartirdge, so that the disk is held on the disk table by the chucking hub so as to become rotatable. Under this state, the disk is rotated as the disk table is rotated and a head assembly is moved so as to correspond to the opening of the disk cartridge to thereby carry out the recording or reproduction.
In the prior art, a magnet chucking system is employed in order to hold the optical disk on the disk table positively and easily. A known chucking hub is made of a metal plate to prevent the magnet chucking hub and its central opening from being abraded away.
Referring to FIG. 1, a chucking hub 2 made of a metal plate (which may be made of a magnetic metal plate or sheet) is fixed to both surfaces of, for example, an optical disk 1 at its central portion. The optical disk 1 is held on a disk table 3 of a recording and reproducing apparatus and a top portion of a disk table shaft 4 is inserted into a central opening 2a of the chucking hub 2, whereby the chucking hub 2 is attracted by an attraction force of a magnet 5 fixed to the inside of the disk table 3, thus the disk 1 being rotated together with the disk table 3.
As FIGS. 1 and 2 illustrate, the chucking hub 2 is formed of a disk-shaped metal plate 6 and a resin layer 7 bonded to the outer peripheral portion of the metal plate 6. The chucking hub 2 is fixed to the disk 1 by welding the resin layer 7 to the disk 1 coated with a resinous material by means of a ultrasonic welding horn 8.
In the thus constructed optical disk 1, the chucking hub 2 is so formed as to allow the resin layer 7 to cover the outer peripheral portion of the disk-shaped metal plate 6 from its peripheral end edge portion of the rear surface. Accordingly, the resin layer 7 is molded on the disk-shaped metal plate 6 by a molding process. Therefore, the chucking hub 2 can not be mass-produced, but must be manufactured one by one, so that its cost is increased. Further, the resin layer 7 is flush with the surface of the disk-shaped metal plate 6, so that in the welding process, the ultrasonic welding horn 8 directly contacts with the surface of the chucking hub 2, or the surface of the disk-shaped metal plate 6. Thus, the ultrasonic welding horn 8 is abraded away considerably. Also, in the welding process, the vibration of this metal plate 6 and the ultrasonic welding horn 8 causes abnormal sound to emanate.
Furthermore, the resin layer 7 is bonded to the disk-shaped metal plate 6 only on its rear surface, outer peripheral end edge surface and the inner peripheral surface of an opening 6a bored through the metal plate 6, i.e. only on the resin layer 7 which is opposed to the chucking surface of the chucking hub 2 and its thickest portion. Thus, resin layer 7 is bonded to the metal plate 6 with a poor bonding strength and the disk-shaped metal plate 6 will peel or detach from the resin layer 7, or the chucking hub 2 will be broken when the optical disk 1 frequently loaded onto or unloaded from the disk table 3.